Turbochargers are provided on an engine to deliver air to the engine intake at a greater density than would be possible in a normal aspirated configuration. This allows more fuel to be combusted, thus boosting the engine's horsepower without significantly increasing engine weight.
Generally, turbochargers use the exhaust flow from the engine exhaust manifold, which enters the turbine stage of the turbocharger at a turbine housing inlet, to thereby drive a turbine wheel, which is located in the turbine housing. The turbine wheel is affixed to one end of a shaft that is rotatably supported within a bearing housing. The shaft drives a compressor impeller mounted on the other end of the shaft. As such, the turbine wheel provides rotational power to drive the compressor impeller and thereby drive the compressor of the turbocharger. This compressed air is then provided to the engine intake as described above.
The compressor stage of the turbocharger comprises the compressor impeller and its associated compressor housing. Filtered air is drawn axially into a compressor air inlet which defines a passage extending axially to the compressor impeller. Rotation of the compressor impeller pressurizes air, creating a radially outward flow from the compressor impeller into the compressor volute for flow to the engine.
Pressure conditions in the turbine stage and compressor stage can often result in oil being drawn through the mechanisms that seal the rotating assembly to the bearing housing. The internal flow of oil from the bearing housing to the compressor stage and engine combustion chamber is generally referred to as “compressor end oil-passage.” Compressor-end oil passage is to be avoided as it can result in contamination of the catalysts and unwanted emissions. With ever more stringent emissions standards, the propensity for compressor-end oil passage is becoming a greater issue.
Thus, there is a need for enhanced sealing arrangements between the rotating components and the static components in the compressor-end of a turbocharger, particularly at low turbocharger speeds.